Technical Field
The subject invention is directed toward a compressor having a clutch mechanism for translating torque between an input power source and a compressor drive shaft where the clutch is initially electromagnetically actuated to begin torque translation and then responsive to a compressor discharge pressure to bring about full torque translation between the input power source and the compressor drive shaft to actuate the compressor.
Description of the Prior Art
Fluid pumping assemblies such as refrigerant compressors used for compressing a recirculating refrigerant in automotive air conditioning systems generally include some type of clutch mechanism to translate power from a power input source to the drive shaft of the compressor. One standard clutch mechanism commonly in use today includes a continuously driven pulley which is rotatably supported about a tubular extension of a clutch housing via ball bearings. The pulley is driven from the power take off of an automotive engine using a belt in the form of an endless loop as is commonly known in the art. An electromagnetic coil or solenoid generates an electromagnetic force which acts to draw an armature plate across a predetermined gap into frictional engagement with a rotating clutch friction plate. The armature plate is movably mounted to a hub using springs or an elastomeric support member. The hub, in turn, is fastened to a compressor drive shaft. When the coil is energized, the clutch friction plate imparts rotation to the armature plate which, in turn, causes the hub and the compressor drive shaft to rotate thereby driving the compressor.
Examples of electromagnetically actuated clutches employed with refrigerant compressors can be found at U.S. Pat. No. 4,296,851, issued to Pierce on Oct. 27, 1981; U.S. Pat. No. 4,616,742 issued to Matsushita on Oct. 14, 1986 and the clutches disclosed in pending United States patent applications entitled "High Dampening Soft Torque Cushion With Buckling Constraints" and "Clutch Field Operated Oil Injector Valve", both of which are assigned to the assignee of the subject invention.
Unfortunately, the friction load generated between the clutch friction plate and the armature can be very high and often dictate the use of relatively large solenoid coils in order to generate enough electromagnetic force to pull the armature plate across the gap and into frictional engagement with the clutch friction plate. Additionally, and because of the relatively high loads involved, the armature and clutch friction plates are areas of premature wear and failure.
In addition, the externally mounted, dry, electromagnetic clutches are not tolerant of slow engagement which is a desirable characteristic to the consumer. Such clutches wear excessively if engaged slowly. The provision of slow engagement also increases the cost of the electrical control means.
Other clutch mechanisms have been disclosed which employ the compressor discharge pressure to cause frictional engagement between adjacent clutch plates thereby translating torque between an input and output shaft. One such example of this type of clutch mechanism can be found in U.S. Pat. No. 4,715,800 issued to Nishizawa et al on Dec. 29, 1987 and its divisional U.S. Pat. No. 4,828,463 issued on May 9, 1989. The disclosure of both of the Nishizawa patents are identical and therefore will be discussed collectively.
The Nishizawa '800 and '463 patents are directed toward a rotary compressor with a clutch and bypass control actuated by hydraulic and/or compressed fluid. More specifically, these patents disclose a compressor having an electromagnetically actuated valve which controls the flow from a continuously driven small trochoid pump which generates a hydraulic discharge pressure which acts on a pressure responsive clutch plate to cause an initial drive of the compressor. The compressor discharge pressure is then employed to act on the pressure responsive clutch plate to cause full clutch engagement to drive the compressor.
The Nishizawa '800 and '463 compressors do not disclose the use of an electromagnetic force to cause initial clutch actuation. Further, the porting necessary to cause clutch actuation using a hydraulic fluid as well as a refrigerant discharge pressure is rather complex and increases the cost of such compressors.